Lens unit and see-through type display apparatus including the same

ABSTRACT

A see-through type display apparatus includes a see-through type optical system configured to transmit a first image via a first-path light, which is light traveling on a first path, to an ocular organ of a user, and a second image via a second-path light, which is light traveling on a second path, to the ocular organ of the user; and an incident light-dependent lens unit provided between the see-through type optical system and the ocular organ of the user and having different refractive powers according to characteristics of incident light, where the incident light-dependent lens unit has a positive first refractive power with respect to the first-path light and has a second refractive power different from the first refractive power with respect to the second-path light.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Divisional Application of U.S. application Ser.No. 15/788,402, filed Oct. 19, 2017, which claims priority from KoreanPatent Application No. 10-2016-0135926, filed on Oct. 19, 2016 in theKorean Intellectual Property Office, the disclosure of which isincorporated herein in its entirety by reference.

BACKGROUND 1. Field

Example embodiments of the present disclosure relate to optical elementsand display apparatuses including the same, and more particularly, tolens units and see-through type display apparatuses including the same.

2. Description of the Related Art

Recently, as electronic apparatuses and display apparatuses capable ofgenerating virtual reality (VR) have been developed, interest in suchapparatuses has increased. As a next step of VR, technologies or methodsto generate augmented reality (AR) and mixed reality (MR) have beenresearched.

Unlike VR that is completely based on a virtual world, AR is a displaytechnology that shows the real world in combination with virtual objectsor information overlapped thereon, thereby further increasing therealistic effects. While VR is generally limited to fields such as gamesor virtual experience, AR may be applied to various environments in thereal world. In particular, AR has attracted attention as thenext-generation display technology suitable for a ubiquitous environmentor an Internet of Things (IoT) environment. AR may be an example of MRas AR presents a mixture of the real world and additional information(i.e., the virtual world).

SUMMARY

One or more example embodiments provide see-through type displayapparatuses that may be applied to implement (generate) augmentedreality (AR) or mixed reality (MR).

One or more example embodiments also provide see-through type displayapparatuses having excellent performance.

One or more example embodiments also provide see-through type displayapparatuses that have a wide viewing angle (or angle of view).

One or more example embodiments also provide see-through type displayapparatuses having a compact configuration.

One or more example embodiments also provide lens units that may beapplied to the see-through type display apparatuses.

One or more example embodiments also provide lens units having a focallength varying according to characteristics of incident light.

One or more example embodiments also provide electronic apparatusesincluding the see-through type display apparatuses.

According to an aspect of an example embodiment, there is provided asee-through type display apparatus including: a see-through type opticalsystem configured to transmit a first image via a first-path light,which is light traveling on a first path, to an ocular organ of a user,and a second image via a second-path light, which is light traveling ona second path, to the ocular organ of the user; and an incidentlight-dependent lens unit provided between the see-through type opticalsystem and the ocular organ of the user and having different refractivepowers according to characteristics of incident light, wherein theincident light-dependent lens unit has a positive first refractive powerwith respect to the first-path light and has a second refractive powerdifferent from the first refractive power with respect to thesecond-path light.

The incident light-dependent lens unit may have a refractive power equalto 0 or substantially equal to 0 with respect to the second-path light.

The incident light-dependent lens unit may be configured to havedifferent refractive powers according to polarization directions of theincident light.

The incident light-dependent lens unit may include: a first lens havinga focal length varying according to polarization directions of theincident light; and a second lens provided adjacent to the first lensand having a constant focal length regardless of the polarizationdirections of the incident light.

The first lens may have a positive first focal length with respect tothe first-path light when the first-path light is incident on the firstlens and has a first polarization direction and may have a negativesecond focal length with respect to the second-path light when thesecond-path light is incident on the first lens and has a secondpolarization direction, and the second lens may have a positive thirdfocal length with respect to the first-path light when the first-pathlight is incident on the second lens and has the first polarizationdirection and the second-path light when the second-path light isincident on the second lens and has the second polarization direction.

An absolute value of the first focal length and an absolute value of thesecond focal length may be equal to each other.

An absolute value of the second focal length and an absolute value ofthe third focal length may be equal to each other.

The incident light-dependent lens unit may have a focal lengthcorresponding to half (½) of the first focal length with respect to thefirst-path light having the first polarization direction, and theincident light-dependent lens unit may have an infinite or substantiallyinfinite focal length with respect to the second-path light having thesecond polarization direction.

The first polarization direction and the second polarization directionmay be orthogonal to each other.

The first lens may be a flat plate type lens, and the second lens may bea convex lens.

The first image may be an image formed and provided by the see-throughtype display apparatus, and the second image may be an outside imagethat the user faces through the see-through type display apparatus.

The see-through type optical system may include: an image forming deviceconfigured to form the first image; and a polarization beam splitter(PBS) configured to transmit the first image formed by the image formingdevice to the ocular organ of the user, wherein the second image may betransmitted through the PBS to the ocular organ of the user.

The see-through type optical system may further include a quarter-waveplate (QWP) arranged between the polarization beam splitter (PBS) andthe incident light-dependent lens unit.

The see-through type optical system may include: an image forming deviceconfigured to form the first image; a transflective member configured totransmit the first image formed by the image forming device to theocular organ of the user; a first polarizer provided between thetransflective member and the image forming device; and a secondpolarizer facing the incident light-dependent lens unit with thetransflective member interposed between the second polarizer and theincident light-dependent lens unit, wherein the second image may betransmitted through the transflective member to the ocular organ of theuser.

The see-through type optical system may further include a quarter-waveplate (QWP) provided between the transflective member and the incidentlight-dependent lens unit.

The see-through type optical system may include: a transparent imageforming device configured to form the first image; and a polarizerfacing the incident light-dependent lens unit with the transparent imageforming device interposed between the polarizer and the incidentlight-dependent lens unit, wherein the second image may be transmittedthrough the transparent image forming device to the ocular organ of theuser.

The see-through type optical system may further include a quarter-waveplate (QWP) provided between the transparent image forming device andthe incident light-dependent lens unit.

The see-through type display apparatus may have an angle of view greaterthan or equal to about 40°.

The see-through type display apparatus may be configured to implementaugmented reality (AR) or mixed reality (MR).

The see-through type display apparatus may be a head mounted display(HMD).

The see-through type display apparatus may be a glasses-type display ora goggle-type display.

According to an aspect of another example embodiment, there is provideda see-through type display apparatus including: a see-through typeoptical system configured to transmit a first image by a first-pathlight, which is light traveling on a first path, to an ocular organ of auser, and a second image by a second-path light, which is lighttraveling on a second path, to the ocular organ of the user; and anincident light-dependent lens unit provided between the see-through typeoptical system and the ocular organ of the user and having differentcharacteristics according to polarization directions of incident light,wherein the incident light-dependent lens unit includes: a first lenshaving a focal length varying according to the polarization directionsof the incident light; and a second lens joined to the first lens andhaving a constant focal length regardless of the polarization directionsof the incident light.

The incident light-dependent lens unit may function as a convex lenswith respect to the first-path light and function as a flat plate withrespect to the second-path light.

The first lens may have a positive first focal length with respect tothe first-path light when the first-path light is incident on the firstlens and has a first polarization direction and may have a negativesecond focal length with respect to the second-path light when thesecond-path light is incident on the first lens and has a secondpolarization direction, and the second lens may have a positive thirdfocal length with respect to the first-path light when the first-pathlight is incident on the second lens and has the first polarizationdirection and the second-path light when the second-path light isincident on the second lens and has the second polarization direction.

An absolute value of the first focal length and an absolute value of thesecond focal length may be equal to each other, and an absolute value ofthe second focal length and an absolute value of the third focal lengthmay be equal to each other.

According to an aspect of another example embodiment, there is provideda compound lens unit including: a first lens having a focal lengthvarying according to polarization directions of incident light; and asecond lens joined to the first lens and having a constant focal lengthregardless of the polarization directions of the incident light.

The first lens may have a positive first focal length with respect to anincident light having a first polarization direction and may have anegative second focal length with respect to an incident light having asecond polarization direction, and the second lens may have a positivethird focal length with respect to the incident light having the firstpolarization direction and the incident light having the secondpolarization direction.

An absolute value of the first focal length and an absolute value of thesecond focal length may be equal to each other.

An absolute value of the second focal length and an absolute value ofthe third focal length may be equal to each other.

The first lens may be a flat plate type lens, and the second lens may bea convex lens.

The compound lens unit may function as a convex lens with respect to anincident light having a first polarization direction and may function asa flat plate with respect to an incident light having a secondpolarization direction orthogonal to the first polarization direction.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawing(s) will be provided by the Office upon request and paymentof the necessary fee.

The above and/or other aspects will become apparent and more readilyappreciated from the following description of example embodiments, takenin conjunction with the accompanying drawings in which:

FIG. 1 schematically illustrates a see-through type display apparatusaccording to an example embodiment;

FIGS. 2A and 2B illustrate the principle and function of the see-throughtype display apparatus of FIG. 1;

FIGS. 3A and 3B illustrate the features of a first lens applicable to alens unit of a see-through type display apparatus according to anexample embodiment;

FIG. 4 illustrates the features of a second lens applicable to a lensunit of a see-through type display apparatus according to an exampleembodiment;

FIGS. 5A and 5B illustrate the features of a compound lens unitcorresponding to a combination of a first lens and a second lensapplicable to a see-through type display apparatus according to anexample embodiment;

FIG. 6 is a plan view illustrating an example of the configuration of afirst lens applicable to a lens unit of a see-through type displayapparatus according to an example embodiment;

FIG. 7 is a cross-sectional view illustrating the configuration of alens unit applicable to a see-through type display apparatus accordingto another example embodiment;

FIG. 8 is a cross-sectional view illustrating the configuration of alens unit applicable to a see-through type display apparatus accordingto another example embodiment;

FIG. 9 is a picture illustrating an example of a lens unit applicable toa see-through type display apparatus according to an example embodiment;

FIG. 10 is a picture illustrating basic experimental results forevaluating the characteristics of the lens unit of FIG. 9;

FIG. 11 illustrates an example of the configuration of a see-throughtype display apparatus according to an example embodiment;

FIG. 12 illustrates an example of the configuration of a see-throughtype display apparatus according to another example embodiment;

FIG. 13 illustrates an example of the configuration of a see-throughtype display apparatus according to another example embodiment;

FIG. 14 is a cross-sectional view illustrating an example of theconfiguration of a transparent image forming device and a polarizer ofFIG. 13;

FIG. 15 illustrates an example of the configuration of a see-throughtype display apparatus according to another example embodiment;

FIG. 16 illustrates an example of the configuration of a see-throughtype display apparatus according to another example embodiment;

FIG. 17 illustrates an example of the configuration of a see-throughtype display apparatus according to another example embodiment;

FIGS. 18A and 18B illustrate a see-through type display apparatusaccording to another example embodiment;

FIG. 19 is a block diagram schematically illustrating an overallstructure or system of a see-through type display apparatus according toan example embodiment;

FIG. 20 is a block diagram schematically illustrating an overallstructure or system of a see-through type display apparatus according toanother example embodiment;

FIG. 21 is a block diagram schematically illustrating an overallstructure or system of a see-through type display apparatus according toanother example embodiment;

FIG. 22 is a block diagram schematically illustrating an overallstructure or system of a see-through type display apparatus according toanother example embodiment; and

FIGS. 23, 24, and 25 illustrate various electronic apparatuses to whichsee-through type display apparatuses according to example embodimentsare applicable.

DETAILED DESCRIPTION

Reference will now be made in detail to example embodiments, examples ofwhich are illustrated in the accompanying drawings. In this regard, theactual embodiments may have different forms and should not be construedas being limited to the example descriptions set forth herein.Accordingly, the embodiments described below by referring to the figuresmerely explain example aspects and do not limit the scope of this patentapplication. As used herein, the term “and/or” includes any and allcombinations of one or more of the associated listed items. Expressionssuch as “at least one of,” when preceding a list of elements, modify theentire list of elements and do not modify the individual elements of thelist.

It will be understood that when an element is referred to as being“connected” or “coupled” to another element, the element may be directlyconnected or coupled to the other element or intervening elements may bepresent. In contrast, when an element is referred to as being “directlyconnected” or “directly coupled” to another element, there are nointervening elements present. As used herein the term “and/or” includesany and all combinations of one or more of the associated listed items.

It will be understood that, although the terms “first”, “second”, etc.may be used herein to describe various elements, components, regions,layers and/or sections, these elements, components, regions, layersand/or sections should not be limited by these terms. These terms areonly used to distinguish one element, component, region, layer orsection from another element, component, region, layer or section. Thus,a first element, component, region, layer or section discussed belowcould be termed a second element, component, region, layer or sectionwithout departing from the teachings of example embodiments.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper” and the like, may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. For example, if the device in thefigures is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the exemplary term “below” may encompass both anorientation of above and below. The device may be otherwise oriented(rotated 90 degrees or at other orientations) and the spatially relativedescriptors used herein interpreted accordingly.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of exampleembodiments. As used herein, the singular forms “a,” “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises” and/or “comprising,” when used in this specification,specify the presence of stated features, integers, steps, operations,elements, and/or components, but do not preclude the presence oraddition of one or more other features, integers, steps, operations,elements, components, and/or groups thereof.

Example embodiments are described herein with reference tocross-sectional illustrations that are schematic illustrations ofidealized embodiments (and intermediate structures) of exampleembodiments. As such, variations from the shapes of the illustrations asa result, for example, of manufacturing techniques and/or tolerances,are to be expected. Thus, example embodiments should not be construed asbeing limited to the particular shapes of regions illustrated herein,and instead may include deviations in shapes that result, for example,from manufacturing. Thus, the regions illustrated in the figures areschematic in nature and their shapes are not intended to illustrate theactual shape of a region of a device and are not intended to limit thescope of example embodiments.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which the example embodiments belong. Itwill be further understood that terms, such as those defined incommonly-used dictionaries, should be interpreted as having a meaningthat is consistent with their meaning in the context of the relevant artand will not be interpreted in an idealized or overly formal senseunless expressly so defined herein.

Hereinafter, lens units according to example embodiments, see-throughtype display apparatuses including the lens units, and electronicapparatuses including the same will be described in detail withreference to the accompanying drawings. The widths and thicknesses oflayers or regions illustrated in the accompanying drawings may beexaggerated for clarity and convenience of description. Like referencenumerals may denote like elements throughout the specification.

FIG. 1 schematically illustrates a see-through type display apparatusaccording to an example embodiment.

Referring to FIG. 1, the see-through type display apparatus may includea see-through type optical system ST10. The see-through type opticalsystem ST10 may transmit a plurality of images via a plurality of pathsto an ocular organ 10 of a user, that is, an eye having a pupil 5. Forexample, the see-through type optical system ST10 may transmit or guidea first image via a first-path light L1 and a second image via asecond-path light L2 to the ocular organ 10. Any one of the first-pathlight L1 and the second-path light L2, for example, the second-pathlight L2, may be transmitted through the see-through type optical systemST10. In this case, the first-path light L1 may travel along a differentpath than the second-path light L2. For example, the first-path light L1may be reflected by the see-through type optical system ST10. A detailedconfiguration of the see-through type optical system ST10 will bedescribed later in detail with reference to FIGS. 11 to 18.

The see-through type display apparatus according to the present exampleembodiment may include a lens unit (also referred to as a lens portion)LU10 arranged between the see-through type optical system ST10 and theocular organ 10 of the user. The lens unit LU10 may exhibit differentrefractive powers according to the characteristics of light incidentthereon (e.g., incident light). For example, the lens unit LU10 mayexhibit different refractive powers according to polarization directionsof the incident light. Thus, the lens unit LU10 may be referred to as anincident light-dependent lens unit or a polarization-dependent lensunit. The lens unit LU10 may have a positive (+) first refractive powerwith respect to the first-path light L1 and may have a second refractivepower different from the first refractive power with respect to thesecond-path light L2. The lens unit LU10 may have a refractive powerequal to 0 or substantially equal to 0 with respect to the second-pathlight L2. Thus, the lens unit LU10 may function as a lens having apositive (+) refractive power with respect to the first-path light L1and function as a flat plate (transparent medium) with respect to thesecond-path light L2. The flat plate may be an element different from alens and may be a plate (e.g., transparent plate) that does notsubstantially converge or diverge the incident light. Herein, thefirst-path light L1 and the second-path light L2 may be incident on thelens unit LU10 while having different characteristics, for example,different polarization directions.

The lens unit LU10 may include a plurality of lenses Ln1 and Ln2. Inthis respect, the lens unit LU10 may be referred to as a compound lensunit. For example, the lens unit LU10 may include at least two lenses, afirst lens Ln1 and a second lens Ln2. The second lens Ln2 may beprovided adjacent to the first lens Ln1. For example, the second lensLn2 may be joined to the first lens Ln1. In this case, the first lensLn1 and the second lens Ln2 may be referred to as constituting a doubletlens, such as a cemented doublet lens (e.g., junction lens). Asillustrated herein, the first lens Ln1 may be arranged nearer to theocular organ 10 than the second lens Ln2, or vice versa. That is, thelens unit LU10 may be arranged in a position rotated by 180° withrespect to a vertical center axis thereof. The first lens Ln1 may have afocal length varying according to the characteristics (e.g.,polarization directions) of incident light. The second lens Ln2 may havea constant focal length regardless of the characteristics (e.g.,polarization directions) of incident light. The respective features ofthe first lens Ln1, the second lens Ln2, and the lens unit LU10corresponding to a combination thereof will be described later in detailwith reference to FIGS. 3A to 5B.

The first image transmitted by the first-path light L1 may be an imageformed and provided by the see-through type display apparatus. The firstimage may include virtual reality or virtual information as a displayimage. The second image transmitted by the second-path light L2 may bean outside image that the user faces through the see-through typedisplay apparatus. The second image may include a foreground image thatthe user faces, and a certain background subject. The second image maybe an image of the real world. Thus, the see-through type displayapparatus according to the present example embodiment may be applied togenerate augmented reality (AR) or mixed reality (MR).

Hereinafter, how the lens unit LU10 (the incident light-dependent lensunit) functions differently with respect to the first-path light L1 andthe second-path light L2 will be described in more detail with referenceto FIGS. 2A and 2B.

As illustrated in FIG. 2A, a first-path light L10 may be incident on thelens unit LU10 while having a first polarization direction. For example,the first-path light L10 may be incident on the lens unit LU10 whilebeing right-handed circularly polarized. In other words, the firstpolarization direction may be right-hand circular polarization (RHCP).The lens unit LU10 may function as a lens having a positive (+)refractive power with respect to the first-path light L10. The lenshaving a positive (+) refractive power may be referred to as a convexlens. The ocular organ 10 of the user may see a display image by thefirst-path light L10 through the lens unit LU10. In this case, since thelens LU10 is arranged near to the ocular organ 10, a focal length of thelens unit LU10 may be relatively small in comparison with a diameter ofthe lens unit LU10. Consequently, a wide viewing angle (or angle of viewor field of view) may be easily secured.

As illustrated in FIG. 2B, a second-path light L20 may be incident onthe lens unit LU10 while having a second polarization direction. Thesecond polarization direction may be orthogonal to the firstpolarization direction. For example, the second-path light L20 may beincident on the lens unit LU10 while being left-handed circularlypolarized. In other words, the second polarization direction may beleft-hand circular polarization (LHCP). The lens unit LU10 may have arefractive power of 0 or substantially 0 with respect to the second-pathlight L20. In other words, the lens unit LU10 may function as a flatplate. In this manner, in the case of seeing a second image by thesecond-path light L20, since the lens unit LU10 may function as a flatplate, the second image may be prevented from being distorted by thelens unit LU10. Thus, the user may see the second image withoutdistortion.

When the first image is a virtual display image and the second image isan image of the real world (image received from the outside), the lensunit LU10 may function as a lens having a positive refractive power withrespect to the display image to increase a viewing angle thereof and mayfunction as a flat plate with respect to the outside image to prevent animage distortion problem thereof. In this manner, the above-describedeffects may be simultaneously obtained due to the incidentlight-dependent characteristics of the lens unit LU10.

For a general see-through type display apparatus, in order to see theoutside image in a see-through manner without distortion, a lens may notbe arranged in front of a user's eye. In other words, a lens distortingthe outside image may not be arranged between the user's eye and theoutside foreground. Thus, a lens to see a virtual display image may needto be arranged by avoiding an area between the user's eye and theoutside foreground (also referred to as an avoidance arrangement). Inthis case, however, since an optical path between the user's eye and thelens may become long, a viewing angle thereof may decrease. For example,when the lens is arranged in a conventional manner, the viewing anglemay be as narrow as about 20°.

However, according to the present example embodiment, since the incidentlight-dependent lens unit LU10 is arranged between the ocular organ 10and the see-through type optical system ST10, the lens unit LU10 mayfunction as a lens (e.g., convex lens) with respect to the display imageand as a flat plate (transparent medium) with respect to the outsideimage. Thus, since the optical path between the ocular organ 10 and thelens unit LU10 may be shortened, a wide viewing angle may be easilysecured. In addition, the outside image may be seen without distortionbecause the lens unit LU10 may function as a flat plate. The see-throughtype display apparatus may have a viewing angle of about 40° or more orabout 60° or more. The viewing angle may be about 100° or more.

Hereinafter, the respective features of the first lens Ln1, the secondlens Ln2, and the lens unit LU10 corresponding to a combination thereofillustrated in FIG. 1 will be described in detail with reference toFIGS. 3A, 3B, 4, 5A, and 5B. FIGS. 3A and 3B illustrate the features ofthe first lens Ln1, FIG. 4 illustrates the features of the second lensLn2, and FIGS. 5A and 5B illustrate the features of the lens unit LU10.

FIGS. 3A and 3B illustrate the features of a first lens Ln10 applicableto a lens unit of a see-through type display apparatus according to anexample embodiment.

Referring to FIG. 3A, the first lens Ln10 may have a positive (+) focallength f₁ with respect to an incident light having a first polarizationdirection. The focal length f₁ will be referred to as a first focallength f₁. Thus, the first lens Ln10 may function as a lens (e.g.,convex lens) having a positive (+) refractive power with respect to theincident light having the first polarization direction. The firstpolarization direction may be, for example, right-hand circularpolarization (RHCP).

Referring to FIG. 3B, the first lens Ln10 may have a negative (−) focallength f₂ with respect to an incident light having a second polarizationdirection. The focal length f₂ will be referred to as a second focallength f₂ . Thus, the first lens Ln10 may function as a lens (e.g.,concave lens) having a negative (−) refractive power with respect to theincident light having the second polarization direction. The secondpolarization direction may be orthogonal to the first polarizationdirection. For example, the second polarization direction may beleft-hand circular polarization (LHCP). Herein, the absolute value ofthe second focal length f₂ may be equal or substantially equal to theabsolute value of the first focal length f₁ . Thus, the first lens Ln10may have focal lengths of the same size but opposite signs with respectto the incident light having the first polarization direction and theincident light having the second polarization direction.

The first lens Ln10 described with reference to FIGS. 3A and 3B mayinclude, for example, a plurality of nonlinear material elements forminga certain pattern. By the pattern of the plurality of nonlinear materialelements, the first lens Ln10 may exhibit features illustrated in FIGS.3A and 3B. Herein, the plurality of nonlinear material elements mayinclude, for example, liquid crystal polymers or the like. The pluralityof nonlinear material elements will be described later in more detailwith reference to FIG. 6.

FIG. 4 illustrates the features of a second lens Ln20 applicable to alens unit of a see-through type display apparatus according to anexample embodiment.

Referring to FIG. 4, the second lens Ln20 may have a constant focallength f₃ regardless of the polarization directions of incident beams oflight. In this respect, the second lens Ln20 may be referred to as anisotropic lens. Thus, the second lens Ln20 may have an equal (orsubstantially equal) focal length f₃ with respect to the incident lighthaving the first polarization direction of FIG. 3A and the incidentlight having the second polarization direction of FIG. 3B. The focallength f₃ will be referred to as a third focal length f₃ . The thirdfocal length f₃ may have a positive (+) value. Thus, the second lensLn20 may be a lens (e.g., convex lens) having a positive (+) refractivepower. The absolute value of the third focal length f₃ may be equal orsubstantially equal to the absolute value of the second focal length f₂of FIG. 3B. Also, the third focal length f₃ may be equal orsubstantially equal to the first focal length f₁ of FIG. 3A.

FIGS. 5A and 5B illustrate the features of a compound lens unit LU11corresponding to a combination of a first lens Ln10 and a second lensLn20 applicable to a see-through type display apparatus according to anexample embodiment. Herein, the first lens Ln10 corresponds to the firstlens Ln10 of FIGS. 3A and 3B, and the second lens Ln20 corresponds tothe second lens Ln20 of FIG. 4.

Referring to FIG. 5A, a lens unit LU11 corresponding to a combination ofa first lens Ln10 and a second lens Ln20 may have a positive (+) focallength f with respect to an incident light having a first polarizationdirection. The incident light having the first polarization directionmay be the same as the incident light having the first polarizationdirection described with reference to FIG. 3A. For example, the firstpolarization direction may be right-hand circular polarization (RHCP).The focal length f of the lens unit LU11 may be smaller than the firstfocal length f₁ of FIG. 3A and may be smaller than the third focallength f₃ of FIG. 4. For example, the focal length f may correspond tothe half (½) of the first focal length f₁ of FIG. 3A. Also, the focallength f may correspond to the half (½) of the third focal length f₃ ofFIG. 4. The first lens Ln10 may have a positive (+) first refractivepower with respect to the incident light having the first polarizationdirection, and the second lens Ln20 may have a positive (+) secondrefractive power with respect to the incident light having the firstpolarization direction. Thus, the lens unit LU11 corresponding to thecombination of the first lens Ln10 and the second lens Ln20 may have athird refractive power corresponding to the sum of the first refractivepower and the second refractive power. The first refractive power andthe second refractive power may be equal or substantially equal to eachother, and in this case, the lens unit LU11 may have a refractive power(the third refractive power) corresponding to two times the firstrefractive power. Therefore, the lens unit LU11 may have the focallength f corresponding to the half (½) of the first focal length f₁ (seeFIG. 3A), which may also be referred to as corresponding to the half (½)of the third focal length f₃ (see FIG. 4).

As illustrated in FIG. 5A, since the lens unit LU11 may have a greatrefractive power (a small focal length) corresponding to two times therefractive power of the first lens Ln10 or the second lens Ln20 withrespect to an incident light having the first polarization direction,the lens unit LU11 may have an excellent viewing angle increasing effectwith respect to the incident light. When a general liquid crystal lensand an isotropic lens are combined together, since a refractive indexdifference between the two lenses may not be great, a large viewingangle may not be easily secured. However, as in the example embodiment,in the case of using the first lens Ln10 having a focal length varyingaccording to the polarization directions of incident light and thesecond lens Ln20 having a constant focal length, since a greatrefractive power (a small focal length) may be easily obtained, theF-number of the lens unit LU11 may be reduced and the viewing angle maybe easily increased. In this regard, the viewing angle of thesee-through type display apparatus illustrated in FIG. 1 may be about40° or more, about 60° or more, or about 100° or more. In addition, whenthe lens unit LU11 illustrated in FIG. 5A is applied to the see-throughtype display apparatus illustrated in FIG. 1, since the distance betweenthe ocular organ 10 and the lens unit LU11 may be, for example, about 10mm to about 40 mm, the focal length f of the lens unit LU11 may be about10 mm to about 40 mm. However, this is merely an example of the focallength f, and the focal length f of the lens unit LU11 may be about 10mm or less or about 40 mm or more.

Referring to FIG. 5B, the lens unit LU11 may have an infinite (∞) orsubstantially infinite (∞) focal length with respect to an incidentlight having a second polarization direction. In other words, the lensunit LU11 may have a refractive power of 0 or substantially 0 withrespect to the incident light having the second polarization direction.The incident light having the second polarization direction may be thesame as the incident light having the second polarization directiondescribed with reference to FIG. 3B. The second polarization directionmay be orthogonal to the first polarization direction. For example, thesecond polarization direction may be left-hand circular polarization(LHCP). Since the first lens Ln10 may have a negative (−) refractivepower with respect to the incident light having the second polarizationdirection (see FIG. 3B), the second lens Ln20 may have a positive (+)refractive power (see FIG. 4), and the absolute value of the negative(−) refractive power and the absolute value of the positive (+)refractive power may be equal to each other, the lens unit LU11corresponding to a combination thereof may have a refractive power of 0or substantially 0 with respect to the incident light having the secondpolarization direction. Thus, the lens unit LU11 may have an infinite(∞) or substantially infinite (∞) focal length with respect to theincident light having the second polarization direction. In other words,the lens unit LU11 may function as a flat plate (e.g., a flattransparent medium) with respect to the incident light having the secondpolarization direction.

Table 1 below summarizes the features of the first lens Ln10, the secondlens Ln20, and the lens unit LU11 corresponding to a combination thereofwith respect to an incident light having a first polarization directionand an incident light having a second polarization direction. The firstpolarization direction and the second polarization direction may beorthogonal to each other.

TABLE 1 Incident Light Incident Light Having First Having SecondPolarization Direction Polarization Direction First Lens (Ln10) f₁ > 0f₂ < 0 Second Lens (Ln20) f₃ > 0 f₃ > 0 Compound Lens Unit f > 0 (e.g.,f = f₁/2) Flat Plate (Transparent) (LU11)

The features described with reference to FIGS. 3A to 5B are summarizedin Table 1 above. The lens unit LU11 may function as a lens having apositive (+) focal length f with respect to the incident light havingthe first polarization direction and may function as a flat plate (e.g.,a transparent piece of glass or plastic) with respect to the incidentlight having the second polarization direction. However, the featuressummarized in Table 1 are merely examples and may vary according tonumerous factors, such as design considerations, materials, etc..

FIG. 6 is a plan view illustrating an example of the configuration of afirst lens Ln10A applicable to a lens unit of a see-through type displayapparatus according to an example embodiment.

Referring to FIG. 6, the first lens Ln10A may include a plurality ofnonlinear material elements n1 forming a certain pattern. The pluralityof nonlinear material elements n1 may include, for example, liquidcrystal polymers. However, this is merely an example, and the materialsof the nonlinear material elements n1 may vary in various ways. Theplurality of nonlinear material elements n1 may form a planar(two-dimensional) pattern and may also form a pattern in a thicknessdirection of the first lens Ln10A in some cases. By a pattern array ofthe nonlinear material elements n1, the first lens Ln10A may exhibitdifferent characteristics according to the polarization directions ofincident light. For example, the first lens Ln10A may have a positive(+) first focal length with respect to an incident light having a firstpolarization direction and may have a negative (−) second focal lengthwith respect to an incident light having a second polarizationdirection. In this case, the absolute value of the first focal lengthand the absolute value of the second focal length may be equal orsubstantially equal to each other.

The first lens Ln10A may have a length and a width of, for example,several mm to tens of mm and may have a small thickness of several mm orless. As an example, the thickness of the first lens Ln10A may besmaller than about 1 mm. Also, the first lens Ln10A may have a flatstructure and may generate no spherical aberration when operating as asingle lens. Additionally, the first lens Ln10A may have flexiblecharacteristics. The focal length (+f) of the first lens Ln10A may beseveral mm to hundreds of mm, although is not limited thereto. Forexample, the focal length (+f) of the first lens Ln10A may be about 10mm to about 100 mm. However, the sizes and features of the first lensLn10A described herein are merely examples and may vary according toexample embodiments.

Although FIGS. 5A and 5B illustrate a case where a plano-convex lens isused as the second lens Ln20, a bi-convex lens may also be used as thesecond lens Ln20 according to another example embodiment. Thisconfiguration will be described below with reference to FIG. 7.

FIG. 7 is a cross-sectional view illustrating the configuration of alens unit LU12 applicable to a see-through type display apparatusaccording to another example embodiment.

Referring to FIG. 7, the lens unit LU12 according to the present exampleembodiment may include a first lens Ln12 and a second lens Ln22. Thesecond lens Ln22 may be a lens having an incident surface and an exitsurface that are both convex. In other words, the second lens Ln22 maybe a bi-convex lens. The first lens Ln12 may be joined to one surface(the incident surface or the exit surface) of the second lens Ln22. Thefirst lens Ln12 may have a configuration and features identical orsimilar to those of the first lenses Ln10 and Ln10A described withreference to FIGS. 3A, 3B, and 6, and may be attached (or joined) to acurved surface (the incident surface or the exit surface) of the secondlens Ln22. Thus, both surfaces (the incident surface or the exitsurface) of the first lens Ln12 may have a curvature similar to theattached surface of the second lens Ln22. Also in this case, the firstlens Ln12 may exhibit the same features as described with reference toFIGS. 3A, 3B, and 6. The effect of the curvature may be compensated byproperly adjusting the pattern of a plurality of nonlinear materialelements included in the first lens Ln12. Also, when there is anaberration of the lens unit LU12, a separate element and/or algorithmmay be introduced to compensate or correct the aberration. This may alsobe true for the lens unit LU11 described with reference to FIGS. 5A and5B.

The respective features of the first lens Ln12, the second lens Ln22,and the lens unit LU12 corresponding to a combination thereofillustrated in FIG. 7 may be the same as those of the first lens Ln10,the second lens Ln20, and the lens unit LU11 illustrated in Table 1.

Although FIGS. 5A, 5B, and 7 illustrate a case where two lenses (Ln10 &Ln20 or Ln12 & Ln22) are used to construct a lens unit (LU11 or LU12),three or more lenses may also be used to construct a lens unit. Anexample thereof is illustrated in FIG. 8.

FIG. 8 is a cross-sectional view illustrating the configuration of alens unit LU13 applicable to a see-through type display apparatusaccording to another example embodiment.

Referring to FIG. 8, the lens unit LU13 may include a first lens Ln13and a second lens Ln23 joined to one surface of the first lens Ln13.Also, the lens unit LU13 may further include a third lens Ln33 joined tothe other surface of the first lens Ln13. The first lens Ln13 may have aconfiguration and features identical or similar to those of the firstlens Ln10 described with reference to FIGS. 3A, 3B, and 6. Thus, thefirst lens Ln13 may have different focal lengths according to thepolarization directions of incident light. Also, the second lens Ln23may have a configuration and features similar to those of the secondlens Ln20 described with reference to FIG. 4. Thus, the second lens Ln23may have a constant focal length regardless of the polarizationdirections of incident light. Also, the third lens Ln33 may have aconfiguration and features similar to those of the second lens Ln20described with reference to FIG. 4. Thus, the third lens Ln33 may have aconstant focal length regardless of the polarization directions ofincident light. The second lens Ln23 may be a plano-convex lens, and thethird lens Ln33 may also be a plano-convex lens.

In the example embodiment of FIG. 8, the sum of the effect of the secondlens Ln23 and the effect of the third lens Ln33 may correspond to theeffect of the second lens Ln20 of FIGS. 5A and 5B. In other words, theeffect of the second lens Ln20 of FIGS. 5A and 5B may be distributed toconstruct the second lens Ln23 and the third lens Ln33 of FIG. 8. Thus,the sum of the refractive power of the second lens Ln23 and therefractive power of the third lens Ln33 illustrated in FIG. 8 maycorrespond to the refractive power of the second lens Ln20 of FIGS. 5Aand 5B. Thus, the features of the lens unit LU13 of FIG. 8 may beidentical or similar to the features of the lens unit LU11 of FIGS. 5Aand 5B.

According to example embodiments, at least one first lens and at leastone second lens may be combined to construct a lens unit. Herein, thefirst lens may be a polarization-dependent lens (e.g., Ln10 of FIGS. 3Aand 3B) that has a focal length varying according to the polarizationdirections of incident light. The second lens may be a lens (e.g., Ln20of FIG. 4) that has a constant focal length regardless of thepolarization directions of incident light. A first lens and a secondlens, or a first lens and a plurality of second lenses, or a pluralityof first lenses and at least one second lens may be combined toconstruct a lens unit. In some cases, a plurality of first lenses and aplurality of second lenses may be combined to construct a lens unit. Inthe case of using a plurality of second lenses, at least one of theplurality of second lenses may be a lens (e.g., convex lens) that has apositive (+) refractive power. In this case, at least one other of theplurality of second lenses may be a lens (e.g., concave lens) that has anegative (−) refractive power. Also, a lens unit (an incidentlight-dependent lens unit) may be implemented in various othercombinations and manners. In the above description of the second lens,the terms “convex lens” and “concave lens” are named according to thesigns of refractive powers and the convex lens and the concave lens maybe spherical lenses or aspherical lenses.

FIG. 9 is a picture illustrating an example of a lens unit applicable toa see-through type display apparatus according to an example embodiment.

Referring to FIG. 9, the lens unit may be a compound lens correspondingto a combination of a plurality of lenses. The lens unit may include afirst lens and a second lens joined thereto. The first lens maycorrespond to the first lens (Ln1, Ln10, Ln10A, or Ln12) described withreference to FIG. 1 or the like. The second lens may correspond to thesecond lens (Ln2, Ln20, or Ln22) described with reference to FIG. 1 orthe like. Thus, the first lens may be a lens having a focal lengthvarying according to the polarization directions of incident light, andthe second lens may be a lens having a constant focal length regardlessof the polarization directions of incident light. The thickness of alens unit corresponding to a combination of the first lens and thesecond lens may be about 10 mm or less, and the diameter of the lensunit may be about 1 inch. The lens unit (e.g., compound lens unit) ofFIG. 9 is made as an example for basic experiments.

FIG. 10 is a picture illustrating basic experimental results forevaluating the characteristics of the lens unit of FIG. 9.

In FIG. 10, (A) corresponds to a case where the lens unit functions in aflat plate (e.g., transparent flat plate) mode, and (B) corresponds to acase where the lens unit functions in a lens (e.g., convex lens) mode.(A) corresponds to a case where a left-handed circularly polarizedincident light is used, and (B) corresponds to a case where aright-handed circularly polarized incident light is used. The lens unitfeatures of (A) may correspond to FIG. 5B, and the lens unit features of(B) may correspond to FIG. 5A. As shown in picture (A), since the lensunit functions as a flat plate, a subject may be seen in its original(or nearly original) size. As shown in picture (B), since the lens unitfunctions as a convex lens, a subject may be seen in a magnified form.From these results, it may be seen that the lens unit according to anexample embodiment may function in a flat plate mode or a lens modeaccording to the characteristics (e.g., polarization characteristics) ofincident light.

FIG. 11 illustrates an example of the configuration of a see-throughtype display apparatus according to an example embodiment.

Referring to FIG. 11, the see-through type display apparatus may includea see-through type optical system ST11. The see-through type opticalsystem ST11 may transmit or guide a first image by a first-path lightL11 and a second image by a second-path light L21 to an ocular organ 10of a user. The see-through type display apparatus may further include alens unit LU10 arranged between the see-through type optical system ST11and the ocular organ 10. The lens unit LU10 may have the sameconfiguration and features as described with reference to FIGS. 2A to10.

An example of the configuration of the see-through type optical systemST11 will be described below. The see-through type optical system ST11may include an image forming device D10 configured to form the firstimage. Also, the see-through type optical system ST11 may include apolarization beam splitter PT10 configured to transmit the first imageformed by the image forming device D10 to the ocular organ 10 of theuser.

The image forming device D10 may include, for example, a spatial lightmodulator (SLM). The SLM may be a transmissive light modulator, areflective light modulator, or a transflective light modulator. As anexample, the SLM may include a liquid crystal on silicon (LCoS) panel, aliquid crystal display (LCD) panel, or a digital light projection (DLP)panel. Herein, the DLP panel may include a digital micromirror device(DMD). FIG. 11 illustrates a case where the image forming device D10includes a transmissive light modulator. A light source unit configuredto radiate light onto the image forming device D10 may be furtherprovided. The image forming device D10 may be arranged between the lightsource unit and the see-through type optical system ST11. In some cases,the image forming device D10 may include a light emitting diode (LED)display device or an organic LED (OLED) display device. The imageforming device D10 may be used to implement a two-dimensional (2D) imageor a three-dimensional (3D) image. Herein, the 3D image may be aholographic image, a stereo image, a light field image, or an integralphotography (IP) image. The image forming device D10 may be referred toas a display device or a micro-display device, and a configuration ofthe image forming device D10 is not limited to the above description andmay vary in various ways.

The polarization beam splitter PT10 may transmit the first image formedby the image forming device D10 to the ocular organ 10 of the user. Thefirst image may be reflected by the polarization beam splitter PT10 andthen transmitted to the ocular organ 10. The second image may betransmitted through the polarization beam splitter PT10 and thentransmitted to the ocular organ 10. Thus, the polarization beam splitterPT10 may be a transflective member. The polarization beam splitter PT10may be a transflective member having a polarization function. Thepolarization beam splitter PT10 may reflect a light having a (1-1)thpolarization direction and transmit a light having a (2-1)thpolarization direction. Thus, by using the polarization beam splitterPT10, a first-path light L11 may travel while being polarized (linearlypolarized) in a (1-1)th direction, for example, a directionperpendicular to a surface of the drawing sheet, and a second-path lightL21 may travel while being polarized (linearly polarized) in a (2-1)thdirection, for example, a direction orthogonal to the (1-1)th direction.For example, the (1-1)th polarization direction may be a horizontaldirection on the drawing, and the (2-1)th polarization direction may bea vertical direction on the drawing.

The see-through type optical system ST11 may further include a waveplate WP10 arranged between the polarization beam splitter PT10 and thelens unit LU10. The wave plate WP10 may be, for example, a quarter-waveplate (QWP). By using the wave plate WP10, the first-path light L11 maybe incident on the lens unit LU10 while being polarized (circularlypolarized) in a (1-2)th direction, and the second-path light L21 may beincident on the lens unit LU10 while being polarized (circularlypolarized) in a (2-2)th direction. The (1-2)th direction and the (2-2)thdirection may be orthogonal to each other. For example, by using thewave plate WP10, the first-path light L11 may be incident on the lensunit LU10 while being right-handed circularly polarized, and thesecond-path light L21 may be incident on the lens unit LU10 while beingleft-handed circularly polarized. The lens unit LU10 may function as alens having a positive (+) refractive power with respect to thefirst-path light L11 and may function as a flat plate having arefractive power of 0 or substantially 0 with respect to the second-pathlight L21.

FIG. 12 illustrates an example of the configuration of a see-throughtype display apparatus according to another example embodiment.

Referring to FIG. 12, a see-through type optical system ST12 of thesee-through type display apparatus may include an image forming deviceD10 configured to form a first image and a transflective member T10configured to transmit the first image formed by the image formingdevice D10 to an ocular organ 10 of a user. The transflective member T10may not have a self-polarization function. The transflective member T10may be, for example, a beam splitter or a transflective film. In thiscase, the see-through type optical system ST12 may further include afirst polarizer P10 provided between the transflective member T10 andthe image forming device D10, and a second polarizer P20 provided toface a lens unit LU10 with the transflective member T10 interposedtherebetween. Also, the see-through type optical system ST12 may furtherinclude a wave plate WP10 as described with reference to FIG. 11. Thewave plate WP10 may be, for example, a quarter-wave plate (QWP).

A first-path light L12 may be polarized (linearly polarized) by thefirst polarizer P10 in a (1-1)th direction, reflected by thetransflective member T10, polarized (circularly polarized) by the waveplate WP10 in a (1-2)th direction, and then incident on the lens unitLU10. A second-path light L22 may be polarized (linearly polarized) bythe second polarizer P20 in a (2-1)th direction, for example, adirection orthogonal to the (1-1)th direction, transmitted through thetransflective member T10, polarized (circularly polarized) by the waveplate WP10 in a (2-2)th direction, and then incident on the lens unitLU10. The (1-2)th direction and the (2-2)th direction may be orthogonalto each other. The lens unit LU10 may function as a lens having apositive (+) refractive power with respect to the first-path light L12and may function as a flat plate having a refractive power of 0 orsubstantially 0 with respect to the second-path light L22. A first image(display image) by the first-path light L12 may be reflected by thetransflective member T10 and then transmitted to the ocular organ 10,and a second image (outside image) by the second-path light L22 may betransmitted through the transflective member T10 and then transmitted tothe ocular organ 10.

FIG. 13 illustrates an example of the configuration of a see-throughtype display apparatus according to another example embodiment.

Referring to FIG. 13, a see-through type optical system ST13 of thesee-through type display apparatus may include a transparent imageforming device TD10 configured to form a first image. The transparentimage forming device TD10 may form an image and transmit light. In thiscase, the transparent image forming device TD10 may be arranged betweenan ocular organ 10 of a user and an outside foreground that the userfaces. The transparent image forming device TD10 may include, forexample, a light emitting diode (LED) display device or an organic LED(OLED) display device. The transparent image forming device TD10 may bea self-luminous device. Also, the transparent image forming device TD10may be configured to emit light polarized in a particular direction. Forthis purpose, the transparent image forming device TD10 may include apolarization layer or a polarization element.

The see-through type optical system ST13 may further include a polarizerP15 provided to face the lens unit LU10 with the transparent imageforming device TD10 interposed therebetween. The polarizer P15 may bereferred to as being arranged between the transparent image formingdevice TD10 and the outside foreground. Also, the see-through typeoptical system ST13 may further include a wave plate WP10 as describedwith reference to FIG. 11. The wave plate WP10 may be, for example, aquarter-wave plate (QWP).

A light L13 generated by the transparent image forming device TD10 maybe referred to as a first-path light, and a light L23 entering fromoutside the see-through type optical system ST13 to be transmittedthrough the see-through type optical system ST13 may be referred to as asecond-path light. Since the first-path light L13 and the second-pathlight L23 are similar in their traveling directions but different intheir generation positions and overall paths, they may be referred to ashaving different paths.

The first-path light L13 may be polarized (linearly polarized) by thetransparent image forming device TD10 in a (1-1)th direction and thenpolarized (circularly polarized) by the wave plate WP10 in a (1-2)thdirection. The second-path light L23 may be polarized (linearlypolarized) by the polarizer P15 in a (2-1)th direction different fromthe (1-1)th direction, transmitted through the transparent image formingdevice TD10, and then polarized (circularly polarized) by the wave plateWP10 in a (2-2)th direction. The (1-1)th direction and the (2-1)thdirection may be orthogonal to each other, and the (1-2)th direction andthe (2-2)th direction may be orthogonal to each other. The lens unitLU10 may function as a lens having a positive (+) refractive power withrespect to the first-path light L13 and may function as a flat platehaving a refractive power of 0 or substantially 0 with respect to thesecond-path light L23. Thus, a wide viewing angle may be secured withrespect to a first image (e.g., display image) by the first-path lightL13, and a distortion problem may be prevented with respect to a secondimage (e.g., outside image) by the second-path light L23.

In addition, as in the present example embodiment, in the case of usingthe transparent image forming device TD10, since the configuration ofthe see-through type optical system ST13 may be simplified, thesee-through type display apparatus may be miniaturized. Thus, thesee-through type display apparatus having a compact configuration may beadvantageously implemented. In some cases, since the wave plate WP10 maynot be used, the configuration of the see-through type optical systemST13 may be further simplified and miniaturized.

FIG. 14 is a cross-sectional view illustrating an example of theconfiguration of the transparent image forming device TD10 and thepolarizer P15 of FIG. 13.

Referring to FIG. 14, the transparent image forming device TD10 mayinclude a plurality of pixels Px1 that are two-dimensionally arranged.Referring to a partial enlarged view of FIG. 14, each pixel Px1 of thetransparent image forming device TD10 may include a light emittingelement LE1. The light emitting element LE1 may be arranged at a centerportion of the pixel Px1, and a pixel (Px1) region around the lightemitting element LE1 may be transparent. The light emitting element LE1may have self-luminous characteristics, and a light L13 for a firstimage may be generated from the light emitting element LE1. Thetransparent image forming device TD10 may have a polarization function.Thus, the light L13 for the first image may be polarized (linearlypolarized) in a (1-1)th direction, for example, a directionperpendicular to a surface of the drawing sheet. For example, apolarization layer may be provided at an exit surface of the lightemitting element LE1, and the light L13 may be polarized by thepolarization layer in the (1-1)th direction. A second-path light L23from outside the polarizer P15 may travel through the polarizer P15 andthe transparent image forming device TD10. The second-path light L23 maybe polarized (linearly polarized) by the polarizer P15 in a (2-1)thdirection, for example, a direction orthogonal to the (1-1)th direction,and the polarized light L23 may travel through the transparent imageforming device TD10. The second-path light L23 may travel through atransparent region around the light emitting element LE1. The detailedconfigurations of the transparent image forming device TD10 and thepolarizer P15 described with reference to FIG. 14 are merely examplesand may vary in various ways.

In the example embodiments of FIGS. 11 and 12, at least one of the lensmay be further provided before or behind the image forming device D10.An example thereof is illustrated in FIG. 15.

FIG. 15 illustrates a case where a lens LS10 is further provided in astructure of FIG. 11. The lens LS10 may be arranged before (the top sideof FIG. 15) the image forming device D10. Thus, the image forming deviceD10 may be arranged between the lens LS10 and the polarization beamsplitter PT10. A light source unit may be further provided before (thetop side of FIG. 15) the lens LS10. Since the lens unit LU10 functionsas a lens with respect to the first-path light L11, the lens LS10 may bereferred to as an additional lens or an auxiliary lens. By using theadditional lens LS10, the numerical aperture (NA) and the focal lengthof an optical system may be adjusted. Herein, although it is illustratedthat the lens LS10 is provided before the image forming device D10, thelens LS10 may also be arranged behind the image forming device D10(under the image forming device D10 on FIG. 15). For example, the lensLS10 may be arranged between the image forming device D10 and thepolarization beam splitter PT10. One or more lenses may be provided bothbefore and behind the image forming device D10. The shape of theadditional lens LS10 illustrated in FIG. 15 is merely an example and mayvary in various ways.

FIG. 16 illustrates an example of the configuration of a see-throughtype display apparatus according to another example embodiment.

Referring to FIG. 16, the see-through type display apparatus accordingto the present example embodiment may be configured to form a virtualimage VD11 of an image forming device D11. For example, a relay opticalsystem RS10 may be used to form a virtual image VD11 of the imageforming device D11. Hereinafter, the virtual image VD11 of the imageforming device D11 will be referred to as a virtual image forming deviceVD11. The virtual image forming device VD11 may be an imaged SLM. Thevirtual image forming device VD11 may be formed in a region adjacent tothe polarization beam splitter PT10.

The relay optical system RS10 may include, for example, a first relaylens LS1, a second relay lens LS2, and a spatial filter SF1 arrangedtherebetween. The first relay lens LS1 may have a first focal length f1,and the second relay lens LS2 may have a second focal length f2. Thespatial filter SF1 may be located at or near the focal plane of thefirst and second relay lenses LS1 and LS2. The spatial filter SF1 mayhave an aperture such as a pinhole and may remove a noise in the lighttransmitted through the first relay lens LS1.

The first focal length f1 of the first relay lens LS1 and the secondfocal length f2 of the second relay lens LS2 may be equal to ordifferent from each other. The size of the virtual image forming deviceVD11 may vary according to the relative size (i.e., ratio) between thefirst focal length f1 and the second focal length f2. For example, whenthe second focal length f2 is greater than the first focal length f1,the virtual image forming device VD11 may be larger than the real imageforming device D11. When the first focal length f1 is greater than thesecond focal length f2, the virtual image forming device VD11 may besmaller than the real image forming device D11. Thus, by adjusting thefirst and second focal lengths f1 and f2, the size of the virtual imageforming device VD11 may be controlled to a desired level. The user maysee a display image obtained through the virtual image forming deviceVD11. However, the configuration of the relay optical system RS10described herein is merely an example and may vary in various ways. Asan example, a reflection member may be used to change the path of thelight output from the relay optical system RS10. The virtual imageforming device VD11 may be formed by the light reflected by thereflection member. In this case, the arrangement relationship betweenthe relay optical system RS10 and the polarization beam splitter PT10may vary from FIG. 16.

According to another example embodiment, at least one additional lensmay be further provided in a structure of FIG. 16. An example thereof isillustrated in FIG. 17.

Referring to FIG. 17, a lens LS11 may be further provided between therelay optical system RS10 and the polarization beam splitter PT10. Thevirtual image forming device VD11 may be formed at the lens LS11 or maybe formed in a region adjacent to the lens LS11. Although FIG. 17illustrates a case where the virtual image forming device VD11 is formedat the lens LS11, the virtual image forming device VD11 may also beformed before or behind the lens LS11. By using the additional lensLS11, the numerical aperture (NA) and the focal length of an opticalsystem may be adjusted.

In the above example embodiments, although it has been described thatthe first-path light (e.g., L10 of FIG. 2A) is circularly polarized inthe first direction and then incident on the lens unit (e.g., LU10 ofFIG. 2A) and the second-path light (e.g., L20 of FIG. 2B) is circularlypolarized in the second direction and then incident on the lens unit(e.g., LU10 of FIG. 2B), the polarization direction (the firstpolarization direction) of the first-path light and the polarizationdirection (the second polarization direction) of the second-path lightmay be modified in various ways. For example, the first-path light maybe linearly polarized in the horizontal (or vertical) direction and thenincident on the lens unit, and the second-path light may be linearlypolarized in the vertical (or horizontal) direction and then incident onthe lens unit. Since the lens unit functions as a lens or a flat plateaccording to light polarization, and since the construction of the lensmay vary, the first polarization direction and the second polarizationdirection may not be limited to particular directions. For example, inFIG. 6, when the pattern of the nonlinear material elements n1 isproperly modified, the lens unit (the compound lens unit) including thefirst lens Ln10A may function as a lens having a positive (+) focallength with respect to the incident light linearly-polarized in thehorizontal (vertical) direction and may function as a flat plate withrespect to the incident light linearly-polarized in the vertical(horizontal) direction. Also, in some cases, the lens unit (the compoundlens unit) may function as a lens with respect to the left-handedcircularly polarized (LHCP) incident light and may function as a flatplate with respect to the right-handed circularly polarized (RHCP)incident light. When the first polarization direction and the secondpolarization direction are orthogonal to each other, they may be appliedto the lens unit according to example embodiments regardless of whichdirections the polarization directions are.

FIGS. 18A and 18B illustrate a see-through type display apparatusaccording to another example embodiment. FIGS. 18A and 18B illustrate acase of a change in the polarization direction of the light L10 and L20in FIGS. 2A and 2B, respectively.

Referring to FIG. 18A, a first-path light L15 may be polarized in afirst direction and then incident on a lens unit LU15. The lens unitLU15 may function as a lens with respect to the first-path light L15.Referring to FIG. 18B, a second-path light L25 may be polarized in asecond direction and then incident on the lens unit LU15. The lens unitLU15 may function as a flat plate with respect to the second-path lightL25. The first direction may be orthogonal to the second direction. Forexample, the first direction may be one of the horizontal and verticaldirections, for example, the horizontal direction, and the seconddirection may be the other of the horizontal and vertical directions,for example, the vertical direction. According to the configurations ofa first lens Ln1′ and a second lens Ln2′ constituting the lens unitLU15, the lens unit LU15 may function as a lens with respect to thelight L15 polarized in the horizontal direction and function as a flatplate with respect to the light L25 polarized in the vertical direction.

In FIGS. 18A and 18B, a reference numeral ST15 denotes a see-throughtype optical system. The see-through type optical system ST15 may have asimilar configuration to the see-through type optical systems ST11,ST12, and ST13 described with reference to FIGS. 11 to 17. However, thesee-through type optical system ST15 may not include the wave plate WP10in each of FIGS. 11 to 17. This omission may be because the see-throughtype optical system ST15 does not need to use the wave plate WP10 tocircularly polarize the light. Thus, the configuration of thesee-through type optical system ST15 may be simplified.

FIG. 19 is a block diagram schematically illustrating an overallstructure or system of a see-through type display apparatus according toan example embodiment.

Referring to FIG. 19, a see-through type optical system 100 may beprovided. A lens unit 200 may be provided between the see-through typeoptical system 100 and an ocular organ 10 of a user. The see-throughtype optical system 100 and the lens unit 200 may correspondrespectively to the see-through type optical system and the lens unitdescribed with reference to FIGS. 1 to 18. A controller 300 connected tothe see-through type optical system 100 may be provided. The controller300 may control, for example, an image forming device of the see-throughtype optical system 100. Although not illustrated, a light source unitmay be further provided between the see-through type optical system 100and the controller 300. In this case, the controller 300 may beconnected to the see-through type optical system 100 and the lightsource unit.

The structure of FIG. 19 may be provided in one pair that is left-rightsymmetric. An example thereof is illustrated in FIG. 20.

Referring to FIG. 20, a first see-through type optical system 100A, anda first lens unit 200A and a first controller 300A corresponding theretomay be provided. The first lens unit 200A may be arranged between thefirst see-through type optical system 100A and a first ocular organ 10Aof a user. The first ocular organ 10A may be a left eye of the user. Asecond see-through type optical system 100B spaced apart from the firstsee-through type optical system 100A may be provided, and a second lensunit 200B and a second controller 300B corresponding thereto may beprovided. The second lens unit 200B may be arranged between the secondsee-through type optical system 100B and a second ocular organ 10B ofthe user. The second ocular organ 10B may be a right eye of the user.Thus, the structure of FIG. 20 may be applied to a binocular displayapparatus.

Although FIG. 20 illustrates that the first controller 300A and thesecond controller 300B are provided separately from each other, thefirst controller 300A and the second controller 300B may be integratedinto a single controller. An example thereof is illustrated in FIG. 21.Referring to FIG. 21, first and second see-through type optical systems100A and 100B may be connected to a controller 300C. The controller 300Cmay be arranged, for example, between the first see-through type opticalsystem 100A and the second see-through type optical system 100B.

In FIG. 21, the position of the controller 300C may vary in variousways. An example thereof is illustrated in FIG. 22. FIG. 22 illustratesan example of another position of the controller 300C. The position ofthe controller 300C may vary in various ways. Also, in some cases, thecontroller 300C may be connected to the first and second see-throughtype optical systems 100A and 100B in a wireless manner, not in a wiredmanner.

At least a portion of the see-through type display apparatuses accordingto various example embodiments may constitute a wearable device. Inother words, the see-through type display apparatus may be applied to awearable device. As an example, the see-through type display apparatusmay be applied to a head mounted display (HMD). Also, the see-throughtype display apparatus may be applied to a glasses-type display or agoggle-type display. FIGS. 23 to 25 illustrate various electronicapparatuses to which see-through type display apparatuses according toexample embodiments are applicable. The electronic apparatuses of FIGS.23 to 25 are examples of the HMD, the glasses-type display, and thelike. The wearable electronic apparatuses illustrated in FIGS. 23 to 25may be operated in linkage with (or in connection with) smart phones.

In addition, the see-through type display apparatuses according tovarious example embodiments may be provided in smart phones, and thesmart phone may be used as the see-through type display apparatus. Inother words, the see-through type display apparatus may be applied tocompact electronic apparatuses (or mobile electronic apparatuses), notto the wearable devices illustrated in FIGS. 23 to 25. The varioustechnology fields to which the see-through type display apparatusesaccording to the above example embodiments may be applied is varied.Also, the see-through type display apparatuses according to the aboveexample embodiments may be not only be used to implement augmentedreality (AR) or mixed reality (MR), but also may be applied to otherfields. For example, the inventive concept of the present exampleembodiments may be applied to multi-image displays capable ofsimultaneously displaying a plurality of images.

Although many details have been described above, they are not intendedto limit the scope of the inventive concept, and instead should beinterpreted as descriptive examples. For example, those of ordinaryskill in the art will understand that the configurations of the lensunits (or the compound lens units) and the see-through type displayapparatuses described with reference to FIGS. 1 to 25 may be modified invarious ways. As an example, a plurality of lenses (e.g., Ln1 and Ln2)constituting a lens unit (or a compound lens unit) may be spaced apartfrom each other, and a transparent medium may be provided between theplurality of lenses (e.g., Ln1 and Ln2). Also, the absolute value of apositive (+)-direction focal length (e.g., f₁ in FIG. 3A) of the lensand the absolute value of a negative (−)-direction focal length (e.g.,f₂ in FIG. 3B) of the lens may be different from each other. Also, theconfigurations of the see-through type optical systems may be modifiedin various ways. Furthermore, the lens units (or the compound lensunits) may be applied to many other fields other than see-through typedisplay apparatuses, and the application fields of the see-through typedisplay apparatuses may vary in various ways.

While one or more example embodiments have been described with referenceto the figures, it will be understood by those of ordinary skill in theart that various changes in form and details may be made therein withoutdeparting from the spirit and scope as defined by the following claims.

What is claimed is:
 1. A see-through type display apparatus comprising:a see-through type optical system configured to transmit a first imageby a first-path light, which is light traveling on a first path, to anocular organ of a user, and a second image by a second-path light, whichis light traveling on a second path, to the ocular organ of the user;and an incident light-dependent lens unit provided between thesee-through type optical system and the ocular organ of the user andhaving different characteristics according to polarization directions ofincident light, wherein the incident light-dependent lens unitcomprises: a first lens having a focal length varying according to thepolarization directions of the incident light; and a second lens joinedto the first lens and having a constant focal length regardless of thepolarization directions of the incident light.
 2. The see-through typedisplay apparatus of claim 1, wherein the incident light-dependent lensunit is configured to function as a convex lens with respect to thefirst-path light and to function as a flat plate with respect to thesecond-path light.
 3. The see-through type display apparatus of claim 1,wherein the first lens has a positive first focal length with respect tothe first-path light when the first-path light is incident on the firstlens and has a first polarization direction, the first lens has anegative second focal length with respect to the second-path light whenthe second-path light is incident on the first lens and has a secondpolarization direction, the second lens has a positive third focallength with respect to the first-path light when the first-path light isincident on the second lens and has the first polarization direction,and the second lens has the positive third focal length with respect tothe second-path light when the second-path light is incident on thesecond lens and has the second polarization direction.
 4. Thesee-through type display apparatus of claim 3, wherein an absolute valueof the positive first focal length and an absolute value of the negativesecond focal length are equal to each other, and the absolute value ofthe negative second focal length and an absolute value of the positivethird focal length are equal to each other.
 5. A compound lens unitcomprising: a first lens having a focal length that varies according topolarization directions of incident light; and a second lens joined tothe first lens and having a constant focal length regardless of thepolarization directions of the incident light.
 6. The compound lens unitof claim 5, wherein the first lens has a positive first focal lengthwith respect to an incident light having a first polarization directionand has a negative second focal length with respect to an incident lighthaving a second polarization direction, and the second lens has apositive third focal length with respect to the incident light havingthe first polarization direction and the incident light having thesecond polarization direction.
 7. The compound lens unit of claim 6,wherein an absolute value of the positive first focal length and anabsolute value of the negative second focal length are equal to eachother.
 8. The compound lens unit of claim 6, wherein an absolute valueof the negative second focal length and an absolute value of thepositive third focal length are equal to each other.
 9. The compoundlens unit of claim 5, wherein the first lens is a flat plate type lens,and the second lens is a convex lens.
 10. The compound lens unit ofclaim 5, wherein the compound lens unit is configured to function as aconvex lens with respect to an incident light having a firstpolarization direction and to function as a flat plate with respect toan incident light having a second polarization direction orthogonal tothe first polarization direction.